Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants. They can ease symptoms of moderate to severe depression, are relatively safe and typically cause fewer side effects than other types of antidepressants do.

SSRIs ease depression by increasing levels of serotonin in the brain. Serotonin is one of the chemical messengers (neurotransmitters) that carry signals between brain cells. SSRIs block the reabsorption (reuptake) of serotonin in the brain, making more serotonin available. SSRIs are called selective because they seem to primarily affect serotonin, not other neurotransmitters.

SSRIs also may be used to treat conditions other than depression, such as anxiety disorders.

The Food and Drug Administration (FDA) has approved these SSRIs to treat depression:

Citalopram (Celexa)

Escitalopram (Lexapro)

Fluoxetine (Prozac)

Paroxetine (Paxil, Pexeva)

Sertraline (Zoloft)

Vilazodone (Viibryd)

Fluvoxamine, an SSRI that's approved by the FDA to treat obsessive-compulsive disorder, is sometimes used to treat depression.

All SSRIs work in a similar way and generally can cause similar side effects, though some people may not experience any. Many side effects may go away after the first few weeks of treatment, while others may lead you and your doctor to try a different drug. If you can't tolerate one SSRI, you may be able to tolerate a different one, as SSRIs differ in chemical makeup.

Possible side effects of SSRIs may include, among others:

Drowsiness

Nausea

Dry mouth

Insomnia

Diarrhea

Nervousness, agitation or restlessness

Dizziness

Sexual problems, such as reduced sexual desire or difficulty reaching orgasm or inability to maintain an erection (erectile dysfunction)

Headache

Blurred vision

Taking your medication with food may reduce the risk of nausea. Also, as long as your medication doesn't keep you from sleeping, you can reduce the impact of nausea by taking it at bedtime.

Which antidepressant is best for you depends on a number of issues, such as your symptoms and any other health conditions you may have. Ask your doctor and pharmacist about the most common possible side effects for your specific SSRI and read the patient medication guide that comes with the prescription.

SSRIs are generally safe for most people. However, in some circumstances they can cause problems. For example, high doses of citalopram may cause dangerous abnormal heart rhythms, so doses over 40 milligrams (mg) a day should be avoided, according to the FDA and the manufacturer. They also recommend a maximum dose of 20 mg for people over age 60.

Other issues to discuss with your doctor before you take an SSRI include:

Drug interactions. When taking an antidepressant, tell your doctor about any other prescription or over-the-counter medications, herbs or other supplements you're taking. Some antidepressants can cause dangerous reactions when combined with certain medications or herbal supplements.

Serotonin syndrome. Rarely, an antidepressant can cause high levels of serotonin to accumulate in your body. Serotonin syndrome most often occurs when two medications that raise the level of serotonin are combined. These include other antidepressants, certain pain or headache medications, and the herbal supplement St. John's wort. Signs and symptoms of serotonin syndrome include anxiety, agitation, sweating, confusion, tremors, restlessness, lack of coordination and a rapid heart rate. Seek immediate medical attention if you have any of these signs or symptoms.

Antidepressants and pregnancy. Talk to your doctor about the risks and benefits of using specific antidepressants. Some antidepressants may harm your baby if you take them during pregnancy or while you're breast-feeding. If you're taking an antidepressant and you're considering getting pregnant, talk to your doctor about the possible risks. Don't stop taking your medication without contacting your doctor first, as stopping might pose risks for you.

Most antidepressants are generally safe, but the FDA requires that all antidepressants carry black box warnings, the strictest warnings for prescriptions. In some cases, children, teenagers and young adults under 25 may have an increase in suicidal thoughts or behavior when taking antidepressants, especially in the first few weeks after starting or when the dose is changed.

Anyone taking an antidepressant should be watched closely for worsening depression or unusual behavior. If you or someone you know has suicidal thoughts when taking an antidepressant, immediately contact your doctor or get emergency help.

Keep in mind that antidepressants are more likely to reduce suicide risk in the long run by improving mood.

SSRIs aren't considered addictive. However, stopping antidepressant treatment abruptly or missing several doses can cause withdrawal-like symptoms. This is sometimes called discontinuation syndrome. Work with your doctor to gradually and safely decrease your dose.

Withdrawal-like symptoms can include:

General feeling of uneasiness

Nausea

Dizziness

Lethargy

Flu-like symptoms

People may react differently to the same antidepressant. For example, a particular drug may work better — or not as well — for you than for another person. Or you may have more, or fewer, side effects from taking a specific antidepressant than someone else does.

Inherited traits play a role in how antidepressants affect you. In some cases, where available, results of special blood tests may offer clues about how your body may respond to a particular antidepressant. However, other variables besides genetics can affect your response to medication.

When choosing an antidepressant, your doctor takes into account your symptoms, any health problems, other medications you take and what has worked for you in the past.

Typically, it may take several weeks or longer before an antidepressant is fully effective and for initial side effects to ease up. You may need to try several dose adjustments or different antidepressants before you find the right one, but hang in there. With patience, you and your doctor can find a medication that works well for you.

Reprint Permissions

A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.org," "Mayo Clinic Healthy Living," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.